1. Field of the Invention
This invention relates in general to shock absorbers for railway cars, and in particular to an underframe, sliding sill shock absorber.
2. Description of the Prior Art
Rail cars commonly use shock absorbers to avoid excessive shock through the rail car structure and to the lading contained therein. In one type, the shock absorber is located at one end of a rail car and integrated with the coupling structure. In another type, the frame will slide relative to the center sill of the rail car. The center sill is fixed in length, and has ends that protrude from the opposite ends of the frame for connecting to coupling equipment.
A shock absorber is located underneath the frame between two stationary stops which are mounted to the frame. The shock absorber includes a housing that is stationarily secured to the center sill. The housing contains an inner cylinder which has ports in its sidewall and is of smaller diameter than the housing to provide an outer reservoir or outer chamber surrounding the inner cylinder. In the prior art, a single piston slides within the inner cylinder. A single piston shaft extends in both directions from the piston. The ends of the shaft will be spaced closely to the stationary stops.
In one prior art type, a liquid only locates in the inner cylinder and housing. The housing is stationary with the center sill, while the piston shaft moves with the frame. If a shock occurs, the frame and center sill will slide relative to one another, causing the piston to move relative to the cylinder. The restrictive flow of fluid out the ports in the inner cylinder dampens the shock. A large coil spring urges the housing and cylinder to a central position relative to the piston. While workable, the large coil spring is heavy, expensive, and fatigues. In another prior art type, a gas is used rather than a coil spring. That type uses a single piston and shaft. However, because of its shorter length, extensive modification to the rail car is required in order to replace the liquid only type.